Diesel fuel, jet fuel, and other types of fuel are often manufactured or processed to have a specified cloud point or freeze point. The cloud point of a fuel denotes the temperature at which the first solidified wax particles form within the fuel as the temperature of the fuel decreases. The freeze point of a fuel denotes the temperature at which, after solidified wax particles have formed, the last solidified wax particles melt as the temperature of the fuel increases.
Traditional cloud point and freeze point measurements often use changes in optical scattering characteristics of a fuel as the temperature of the fuel is adjusted. However, conventional sensors often times require access to two sides of a fuel sample. This may be difficult or impossible in confined spaces. If access is limited to one side, a reflecting path can be used. Unfortunately, the refractive index of fuel is temperature-dependent, which can lead to misalignment.